Sh
is a command and programming language
that executes commands read from a terminal
or a file.
Rsh
is a restricted version of the
standard
command interpreter
sh;
it is used to set up login names and execution environments whose
capabilities are more controlled than those of the standard shell.
See
Invocation
below
for the meaning of arguments to the shell.

Definitions.

A
metacharacter
is one of the following characters:

; & ( ) | < > new-line space tab

A
blank
is a
tab
or a
space.
An
identifier
is a sequence of letters, digits, or underscores
starting with a letter or underscore.
Identifiers are used as names for
functions
and
variables.
A
word
is a sequence of
characters
separated by one or more non-quoted
metacharacters.

A
command
is a sequence of characters in the syntax
of the shell language.
The shell reads each command and
carries out the desired action either directly or by invoking
separate utilities.
A special command is a command that is carried out by the
shell without creating a separate process.
Except for documented
side effects, most special commands can be implemented as separate
utilities.

Commands.

A
simple-command
is a sequence of
blank
separated words
which may be preceded by a variable assignment list.
(See
Environment
below.)
The first word specifies the name of the command to
be executed.
Except as specified below,
the remaining words are passed as arguments
to the invoked command.
The command name is passed as argument 0
(see
exec(2)).
The
value
of a simple-command is its exit status
if it terminates normally, or (octal) 200+status if
it terminates abnormally (see
signal(2)
for a list of
status values).

A
pipeline
is a sequence of one or more
commands
separated by
|.
The standard output of each command but the last
is connected by a
pipe(2)
to the standard input of the next command.
Each command is run as a separate process;
the shell waits for the last command to terminate.
The exit status of a pipeline is the exit
status of the last command.

A
list
is a sequence of one or more
pipelines
separated by
;,
&,
&&,
or
| |,
and optionally terminated by
;,
&,
or
|&.
Of these five symbols,
;,
&,
and
|&
have equal precedence,
which is lower than that of
&&
and
| |.
The symbols
&&
and
| |
also have equal precedence.
A semicolon
(;)
causes sequential execution of the preceding pipeline; an ampersand
(&)
causes asynchronous execution of the preceding pipeline (i.e., the shell does
not
wait for that pipeline to finish).
The symbol
|&
causes asynchronous execution of the preceding command or pipeline
with a two-way pipe established to the parent shell.
The standard input and output of the spawned command
can be written to and read from by the parent Shell
using the
-p
option of
the special commands
read
and
print
described later.
The symbol
&&
( | | )
causes the
list
following it to be executed only if the preceding
pipeline
returns a zero (non-zero) value.
An arbitrary number of new-lines may appear in a
list,
instead of a semicolon,
to delimit a command.

A
command
is either a simple-command
or one of the following.
Unless otherwise stated,
the value returned by a command is that of the
last simple-command executed in the command.

foridentifier [ inword . . . ] ;dolist ;done

Each time a
for
command is executed,
identifier
is set to the next
word
taken from the
inword
list.
If
in word . . .
is omitted, then
the
for
command executes the dolist once for each positional parameter
that is set
(see
Parameter Substitution
below).
Execution ends when there are no more words in the list.

selectidentifier [ inword . . . ] ;dolist ;done

A
select
command prints on standard error (file descriptor 2), the set of
words,
each preceded by a number.
If
in word . . .
is omitted, then
the
positional parameters
are used instead
(see
Parameter Substitution
below).
The
PS3
prompt is printed
and a line is read from the standard input.
If this line consists of the number
of one of the listed
words,
then the value of the variable
identifier
is set to the
word
corresponding to this number.
If this line is empty the selection list is
printed again.
Otherwise the value of the variable
identifier
is set to
null.
The contents of the line read from standard input is
saved in
the variable
REPLY.
The
list
is executed for each selection until a
break
or
end-of-file
is encountered.
If the
REPLY
variable is set to
null
by the execution of
list,
then the selection list is printed before
displaying the
PS3
prompt for the next selection.

caseword in [ [ ( ]pattern [ | pattern ] . . . )list ;; ] . . . esac

A
case
command executes the
list
associated with the first
pattern
that matches
word.
The form of the patterns is
the same as that used for
file-name generation (see
File Name Generation
below).

iflist ;thenlist [ eliflist ;thenlist ] . . . [ ;elselist ] ;fi

The
list
following if is executed and,
if it
returns a zero exit status, the
list
following
the first
then
is executed.
Otherwise, the
list
following elif
is executed and, if its value is zero,
the
list
following
the next
then
is executed.
Failing that, the
elselist
is executed.
If no
elselist
or
thenlist
is executed, then the
if
command returns a zero exit status.

whilelist ;dolist ;done

untillist ;dolist ;done

A
while
command repeatedly executes the
whilelist
and, if the exit status of the last command in the list is zero, executes
the
dolist;
otherwise the loop terminates.
If no commands in the
dolist
are executed, then the
while
command returns a zero exit status;
until
may be used in place of
while
to negate
the loop termination test.

(list )

Execute
list
in a separate environment.
Note, that if two adjacent open parentheses are
needed for nesting, a space must be inserted to avoid
arithmetic evaluation as described below.

{ list ;}

list
is simply executed.
Note that unlike the metacharacters
(
and
),
{
and
}
are
reserved words
and must occur
at the beginning of a line or after a
;
in order to be recognized.

[[expression ]]

Evaluates
expression
and returns a zero exit status when
expression
is true.
See
Conditional Expressions
below, for a description of
expression.

functionidentifier {list ;}

identifier () {list ;}

Define a function which is referenced by
identifier.
The body of the function is the
list
of commands between
{
and
}.
(See
Functions
below).

time pipeline

The
pipeline
is executed and the elapsed time as well as
the user and system time are printed on standard error.

The following reserved words
are only recognized as the first word of a command
and when not quoted:

if then else elif fi case esac for while until do done { } function select time [[ ]]

Comments.

A word beginning with
#
causes that word and all the following characters up to a new-line
to be ignored.

Aliasing.

The first word of each command is replaced by the text of an
alias
if an
alias
for this word has been defined.
An
alias
name consists of any number of characters excluding metacharacters,
quoting characters,
file expansion characters,
parameter and command substitution
characters,
and
=.
The replacement string can contain any
valid Shell script
including the metacharacters listed above.
The first word of each command in the
replaced text,
other than
any that are in the process of being replaced,
will be tested for aliases.
If the last character of the alias value is a
blank
then the word following the alias will also be checked for alias
substitution.
Aliases can be used to redefine special
builtin commands but cannot be used to redefine
the reserved words listed above.
Aliases can be created, listed, and exported with the
alias
command and can be removed with the
unalias
command.
Exported aliases remain in effect for
scripts invoked by name,
but must be reinitialized for separate invocations
of the Shell (see
Invocation
below).

Aliasing
is performed when
scripts are read,
not while they are executed.
Therefore,
for an alias to take effect
the
alias
definition command has to be executed before
the command which references the alias is read.

Aliases are frequently used as a short hand for full path
names.
An option to the aliasing facility allows the value of the alias
to be automatically set to the full pathname of
the corresponding command.
These aliases are called
tracked
aliases.
The value of a
tracked
alias is defined the first time the corresponding command
is looked up and becomes undefined each time
the
PATH
variable is reset.
These aliases remain
tracked
so that the next
subsequent reference will redefine the value.
Several tracked aliases are compiled into the shell.
The
-h
option of the
set
command makes each referenced command name
into a tracked alias.

The following
exportedaliases
are compiled into the shell
but can be unset or redefined:

After alias substitution is performed, each word
is checked to see if it begins with an unquoted
~.
If it does, then the word up to a
/
is checked to see if it matches a user name in the
/etc/passwd
file.
If a match is found, the
~
and the matched login name are replaced by the
login directory of the matched user.
This is called a
tilde
substitution.
If no match is found, the original text is left unchanged.
A
~
by itself, or in front of a
/,
is replaced by
$HOME.
A
~
followed by a
+
or
-
is replaced by
$PWD
and
$OLDPWD
respectively.

In addition,
tilde
substitution is attempted when
the value of a
variable assignment
begins with a
~.

The standard output from a command enclosed in
parenthesis preceded by a dollar sign (
$( )
)
or a pair of grave accents ( ` ` )
may be used as part or all
of a word;
trailing new-lines are removed.
In the second (archaic) form, the string between the quotes is processed
for special quoting characters before the command is executed. (See
Quoting
below.)
The command substitution
$( cat file )
can be replaced by the equivalent but faster
$( <file ) .
Command substitution of most special commands
that do not perform input/output redirection are
carried out without creating a separate process.

An arithmetic expression enclosed in double
parenthesis preceded by a dollar sign (
$(( ))
)
is replaced by the value of the arithmetic expression
within the double parenthesis.

This feature is only available on
versions of the UNIX operating system that support the
/dev/fd
directory for naming open files.
Each command argument of the form
<(list )
or
>(list )
will run process
list
asynchronously connected to some file in
/dev/fd.
The name of this file will become the argument to the command.
If the form with
>
is selected then writing on this file will provide input for
list.
If
<
is used,
then the file passed as an argument will contain the output of the
list
process.
For example,

paste <(cut -f1file1) <(cut -f3file2) | tee >(process1) >(process2)

cuts
fields 1 and 3 from
the files
file1
and
file2
respectively,
pastes
the results together, and
sends it
to the processes
process1
and
process2,
as well as putting it onto the standard output.
Note that the file, which is passed as an argument to the command,
is a UNIX
pipe(2)
so programs that expect to
lseek(2)
on the file will not work.

A
parameter
is an
identifier,
one or more digits,
or any of the characters
*,
@,
#,
?,
-,
$,
and
!\ .
A
variable
(a parameter denoted by an identifier)
has a
value
and zero or more
attributes.
Variables
can be assigned
values
and
attributes
by using the
typeset
special command.
The attributes supported by the Shell are described
later with the
typeset
special command.
Exported variables pass values and attributes to
the environment.

The shell supports a one-dimensional array facility.
An element of an array variable is referenced by a
subscript.
A
subscript
is denoted by a
[,
followed by an
arithmeticexpression
(see
Arithmetic evaluation
below)
followed by a
].
To assign values to an array, use
set -Anamevalue . . . .
The value of all
subscripts must be in the
range of
0 through 1023.
Arrays need not be declared.
Any reference to a variable
with a valid subscript is
legal and an array will be created if necessary.
Referencing an array without a subscript
is equivalent to referencing the element zero.

The
value
of a
variable
may be assigned by writing:

name=value
[
name=value
] . . .

If the integer attribute,
-i,
is set for
name
the
value
is subject to arithmetic evaluation as described below.

Positional parameters,
parameters denoted by a number,
may be assigned values with the
set
special command.
Parameter
$0
is set from argument zero when the shell
is invoked.

The character
$
is used to introduce substitutable
parameters.

${parameter }

The shell
reads all the characters from
${
to the matching
}
as part of the same word even if it contains
braces or metacharacters.
The value, if any, of the parameter is substituted.
The braces are required when
parameter
is followed by a letter, digit, or underscore
that is not to be interpreted as part of its name
or when a variable is subscripted.
If
parameter
is one or more digits then it is a positional parameter.
A positional parameter of more than one digit must be
enclosed in braces.
If
parameter
is
*
or
@,
then all the positional
parameters, starting with
$1,
are substituted
(separated by a field separator character).
If an array
identifier
with subscript
*
or
@
is used,
then the value
for each of the
elements
is substituted
(separated by a field separator character).

${#parameter }

If
parameter
is
*
or
@,
the number of positional parameters is substituted.
Otherwise, the length of the value of the
parameter
is substituted.

${#identifier[*]}

The number of elements in the array
identifier
is substituted.

${parameter :-word }

If
parameter
is set and is non-null then substitute its value;
otherwise substitute
word.

${parameter :=word }

If
parameter
is not set or is null then set it to
word;
the value of the parameter is then substituted.
Positional parameters may not be assigned to
in this way.

${parameter :?word }

If
parameter
is set and is non-null then substitute its value;
otherwise, print
word
and exit from the shell.
If
word
is omitted then a standard message is printed.

${parameter :+word }

If
parameter
is set and is non-null then substitute
word;
otherwise substitute nothing.

${parameter #pattern }

${parameter ##pattern }

If
the Shell
pattern
matches the beginning of the value of
parameter,
then the value of
this substitution is the value of the
parameter
with the matched portion deleted;
otherwise the value of this
parameter
is substituted.
In the first form the smallest matching pattern is deleted and in the
second form the largest matching pattern is deleted.
The result is unspecified when
parameter
is
@,
*,
or an array variable with subscript
@,
or
*.

${parameter %pattern }

${parameter %%pattern }

If
the Shell
pattern
matches the end of the value of
parameter,
then the value of
this substitution is the value of the
parameter
with the matched part deleted;
otherwise substitute the value of
parameter.
In the first form the smallest matching pattern is deleted and in the
second form the largest matching pattern is deleted.
The result is unspecified when
parameter
is
@,
*,
or an array variable with subscript
@,
or
*.

In the above,
word
is not evaluated unless it is
to be used as the substituted string,
so that, in the following example,
pwd
is executed only if
d
is not set or is null:

echo ${d:- $( pwd ) }

If the colon (
:)
is omitted from the above expressions,
then the shell only checks whether
parameter
is set or not.

The following
parameters
are automatically set by the shell:

#

The number of positional parameters in decimal.

-

Flags supplied to the shell on invocation or by
the
set
command.

?

The decimal value returned by the last executed command.

$

The process number of this shell.

_

Initially, the value of
_
is an absolute pathname of the shell or script being executed
as passed in the
environment.
Subsequently it is assigned the last argument of the previous command.
This parameter is not set for commands which are asynchronous.
This parameter is also used to hold the name of the matching
MAIL
file when checking for mail.

!

The process number of the last background command invoked.

ERRNO

The value of
errno
as set by the most recently failed system call.
This value
is system dependent and is intended for debugging purposes.

LINENO

The line number of the current line within the script or
function being executed.

OLDPWD

The previous working directory set by the
cd
command.

OPTARG

The value of the last option argument processed by the
getopts
special command.

OPTIND

The index of the last option argument processed by the
getopts
special command.

PPID

The process number of the parent of the shell.

PWD

The present working directory set by the
cd
command.

RANDOM

Each time this variable is referenced, a random integer,
uniformly distributed between 0 and 32767, is generated.
The sequence of random numbers can be initialized by assigning
a numeric value to
RANDOM.

REPLY

This variable is set by the
select
statement and by
the
read
special command when no arguments are supplied.

SECONDS

Each time this variable is referenced, the number of
seconds since shell invocation is returned.
If this variable is
assigned a value, then the value returned upon reference will
be the value that was assigned plus the number of seconds since the assignment.

The following
variables
are used by the shell:

CDPATH

The search path for the
cd
command.

COLUMNS

If this variable is set,
the value is used to define the width of the edit window
for the shell edit modes and for printing
select
lists.

EDITOR

If the value of this variable ends in
emacs,
gmacs,
or
vi
and the
VISUAL
variable is not set,
then the corresponding option
(see Special Command
set
below)
will be turned on.

ENV

If this variable is set, then
parameter substitution is performed on
the value to generate
the pathname of the script that will be
executed when the
shell
is invoked.
(See
Invocation
below.)
This file is typically used for
alias
and
function
definitions.

FCEDIT

The default editor name for the
fc
command.

FPATH

The search path for function definitions.
By default the
FPATH
directories are searched after the
PATH
variable.
If an executable file is found, then it is read and executed
in the current environment.
FPATH
is searched before
PATH
when a function with the
-u
attribute is referenced.
The preset alias
autoload
preset alias causes a function with the
-u
attribute to be created.

IFS

Internal field separators,
normally
space,
tab,
and
new-line
that are used to separate command words which result from
command or parameter substitution
and for separating words with the special command
read.
The first character of the
IFS
variable is used to separate arguments for the
"$*"
substitution (See
Quoting
below).

HISTFILE

If this variable is set when the shell is invoked, then
the value is the pathname of the file that will be
used to store the command history.
(See
Command re-entry
below.)

HISTSIZE

If this variable is set when the shell is invoked, then
the number of previously entered commands that
are accessible by this shell
will be greater than or equal to this number.
The default is 128.

HOME

The default argument (home directory) for the
cd
command.

LINES

If this variable is set,
the value is used to determine the column length for printing
select
lists.
Select lists will print vertically until about two-thirds of
LINES
lines are filled.

MAIL

If this variable is set to the name of a mail file
and
the
MAILPATH
variable is not set,
then the shell informs the user of arrival of mail
in the specified file.

MAILCHECK

This variable specifies how often (in seconds) the
shell will check for changes in the modification time
of any of the files specified by the
MAILPATH
or
MAIL
variables.
The default value is 600 seconds.
When the time has elapsed
the shell will check before issuing the next prompt.

MAILPATH

A colon (
:
)
separated list of file names.
If this variable is set
then the shell informs the user of
any modifications to the specified files
that have occurred within the last
MAILCHECK
seconds.
Each file name can be followed by a
?
and a message that will be printed.
The message will undergo parameter substitution
with the variable
$_
defined as the name of the file that has changed.
The default message is
youhavemailin$_ .

PATH

The search path for commands (see
Execution
below).
The user may not change
PATH
if executing under
rsh
(except in
.profile ).

PS1

The value of this variable is expanded for parameter
substitution to define the
primary prompt string which by default is
``$ ''.
The character
!
in the primary prompt string is replaced by the
command
number (see
CommandRe-entry
below).
Two successive occurrences of
!
will produce a single
!
when the prompt string is printed.

PS2

Secondary prompt string, by default
``> ''.

PS3

Selection prompt string
used within a
select
loop, by default
``#? ''.

PS4

The value of this variable is expanded for parameter
substitution and precedes each line of an execution trace.
If omitted, the execution trace prompt is
``+ ''.

SHELL

The pathname of the
shell
is kept in the environment.
At invocation, if the basename of this variable is
rsh,
rksh,
or
krsh,
then the shell becomes restricted.

TMOUT

If set to a value greater than zero,
the shell will terminate if a command is not entered within
the prescribed number of seconds after issuing the
PS1
prompt.
(Note that the shell can be compiled with a maximum bound
for this value which cannot be exceeded.)

VISUAL

If the value of this variable ends in
emacs,
gmacs,
or
vi
then the corresponding option
(see Special Command
set
below)
will be turned on.

The shell gives default values to
PATH, PS1, PS2,
PS3, PS4, MAILCHECK, FCEDIT,
TMOUT and IFS,
while
HOME,SHELLENV
and
MAIL
are
not set at all by the shell (although
HOMEis
set by
login(1)).
On some systems
MAIL
and
SHELL
are also
set by
login(1).

After parameter and command substitution,
the results of substitutions are scanned for the field separator
characters (those found in
IFS \c
)
and split into distinct arguments where such characters are found.
Explicit null arguments ( " " or ' ' ) are retained.
Implicit null arguments
(those resulting from
parameters
that have no values) are removed.

Following substitution, each command
word
is scanned for
the characters
*,
?,
and
[
unless the
-f
option has been
set.
If one of these characters appears
then the word is regarded as a
pattern.
The word is replaced with lexicographically sorted file names that match the pattern.
If no file name is found that matches the pattern, then
the word is left unchanged.
When a
pattern
is used for file name generation,
the character
.
at the start of a file name
or immediately following a
/,
as well as the character
/
itself,
must be matched explicitly.
In other instances of pattern matching the
/
and
.
are not treated specially.

*

Matches any string, including the null string.

?

Matches any single character.

[ . . . ]

Matches any one of the enclosed characters.
A pair of characters separated by
-
matches any
character lexically between the pair, inclusive.
If the first character following the opening "[ "
is a "! " then any character not enclosed is matched.
A
-
can be included in the character set by putting it as the
first or last character.

A
pattern-list
is a list of one or more patterns separated from each other
with a
|.
Composite patterns can be formed with one or more of the following:

?(pattern-list )

Optionally matches any one of the given patterns.

*(pattern-list )

Matches zero or more occurrences of the given patterns.

+(pattern-list )

Matches one or more occurrences of the given patterns.

@(pattern-list )

Matches exactly one of the given patterns.

!(pattern-list )

Matches anything, except one of the given patterns.

Quoting.

Each of the
metacharacters
listed above (See
Definitions
above)
has a special meaning to the shell
and causes termination of a word unless quoted.
A character may be
quoted
(i.e., made to stand for itself)
by preceding
it with a
\.
The pair
\new-line
is removed.
All characters enclosed between a pair of single quote marks ( ' ' ),
are quoted.
A single quote cannot appear within single quotes.
Inside double quote marks
(" "),
parameter and command substitution occur and
\
quotes the characters
\,
`,
",
and
$.
The meaning of
$*
and
$@
is identical when not quoted or when used as a parameter assignment value
or as a file name.
However, when used as a command argument,
"$*"
is equivalent to
"$1d $2d . . .",
where
d
is the first character of the
IFS
variable, whereas
"$@"
is equivalent to
"$1" "$2" . . . .
Inside grave quote marks
(` `)
\
quotes the characters
\,
`,
and
$.
If the grave quotes occur within double quotes then
\
also quotes the character
".

The special meaning of reserved words or aliases can be removed by quoting any
character of the reserved word.
The recognition of function names or special command names listed below
cannot be altered by quoting them.

An ability to perform integer arithmetic
is provided with the special command
let.
Evaluations are performed using
long
arithmetic.
Constants are of the form
[ base# ]n
where
base
is a decimal number between two and thirty-six
representing the arithmetic base
and
n
is a number in that base.
If
base
is omitted
then base 10 is used.

An arithmetic expression uses the same syntax, precedence, and
associativity of
expression as the C language.
All the integral operators,
other than
++,
- -,
?:,
and
,
are supported.
Variables can be referenced by name within an arithmetic expression
without using the parameter substitution syntax.
When a variable is referenced, its value is evaluated as
an arithmetic expression.

An internal integer representation of a
variable
can be specified with the
-i
option of the
typeset
special command.
Arithmetic evaluation is performed on the value of each
assignment to a variable with the
-i
attribute.
If you do not specify an arithmetic base,
the first assignment to the
variable determines the arithmetic base.
This base is
used when
parameter substitution occurs.

Since many of the arithmetic operators require
quoting, an alternative form of the
let
command is provided.
For any command which begins with a
((,
all the characters until a matching
))
are treated as a quoted expression.
More precisely,
((. . .))
is equivalent to
let " . . .".

Prompting.

When used interactively,
the shell prompts with the parameter expanded value of
PS1
before reading a command.
If at any time a new-line is typed and further input is needed
to complete a command, then the secondary prompt
(i.e., the value of
PS2)
is issued.

A
conditional expression
is used with the
[[
compound command to test attributes of files and to compare
strings.
Word splitting and file name generation are
not performed on the words between
[[
and
]].
Each expression can be constructed from one or more
of the following unary or binary expressions:

-afile

True, if
file
exists.

-bfile

True, if
file
exists and is a block special file.

-cfile

True, if
file
exists and is a character special file.

-dfile

True, if
file
exists and is a directory.

-ffile

True, if
file
exists and is an ordinary file.

-gfile

True, if
file
exists and is has its setgid bit set.

-kfile

True, if
file
exists and is has its sticky bit set.

-nstring

True, if length of
string
is non-zero.

-ooption

True, if option named
option
is on.

-pfile

True, if
file
exists and is a fifo special file or a pipe.

-rfile

True, if
file
exists and is readable by current process.

-sfile

True, if
file
exists and has size greater than zero.

-tfildes

True, if file descriptor number
fildes
is open and associated with a terminal device.

-ufile

True, if
file
exists and is has its setuid bit set.

-wfile

True, if
file
exists and is writable by current process.

-xfile

True, if
file
exists and is executable by current process.
If
file
exists and is a directory, then the current process
has permission to search in the directory.

-zstring

True, if length of
string
is zero.

-Lfile

True, if
file
exists and is a symbolic link.

-Ofile

True, if
file
exists and is owned by the effective user id of this process.

-Gfile

True, if
file
exists and its group matches the effective group id of this process.

-Sfile

True, if
file
exists and is a socket.

file1-ntfile2

True, if
file1
exists and is newer than
file2.

file1-otfile2

True, if
file1
exists and is older than
file2.

file1-effile2

True, if
file1
and
file2
exist and refer to the same file.

string=pattern

True, if
string
matches
pattern.

string!=pattern

True, if
string
does not match
pattern.

string1<string2

True, if
string1
comes before
string2
based on ASCII value of their characters.

string1>string2

True, if
string1
comes after
string2
based on ASCII value of their characters.

exp1-eqexp2

True, if
exp1
is equal to
exp2.

exp1-neexp2

True, if
exp1
is not equal to
exp2.

exp1-ltexp2

True, if
exp1
is less than
exp2.

exp1-gtexp2

True, if
exp1
is greater than
exp2.

exp1-leexp2

True, if
exp1
is less than or equal to
exp2.

exp1-geexp2

True, if
exp1
is greater than or equal to
exp2.

In each of the above expressions, if
file
is of the form
/dev/fd/n,
where
n
is an integer,
then the test is applied to the open file whose
descriptor number is
n.

A compound expression can be constructed from these primitives by
using any of the following, listed in decreasing order of precedence.

(expression)

True, if
expression
is true.
Used to group expressions.

!expression

True if
expression
is false.

expression1&&expression2

True, if
expression1
and
expression2
are both true.

expression1||expression2

True, if either
expression1
or
expression2
is true.

Input/Output.

Before a command is executed, its input and output
may be redirected using a special notation interpreted by the shell.
The following may appear anywhere in a simple-command
or may precede or follow a
command
and are
not
passed on to the invoked command.
Command and parameter substitution occur before
word
or
digit
is used except as noted below.
File name generation
occurs only if the pattern matches a single file,
and blank interpretation is not performed.

<word

Use file
word
as standard input (file descriptor 0).

>word

Use file
word
as standard output (file descriptor 1).
If the file does not exist then it is created.
If the file exists, and the
noclobber
option is on,
this causes an error;
otherwise, it is truncated to zero length.

>|word

Sames as
>,
except that it overrides the
noclobber
option.

>>word

Use file
word
as standard output.
If the file exists then output is appended to it (by first seeking to the end-of-file);
otherwise, the file is created.

<>word

Open file
word
for reading and writing
as standard input.

<<[ - ]word

The shell input is read up to a line that is the same as
word,
or to an end-of-file.
No parameter substitution, command substitution or
file name generation is performed on
word.
The resulting document,
called a
here-document,
becomes
the standard input.
If any character of
word
is quoted, then no interpretation
is placed upon the characters of the document;
otherwise, parameter and command substitution occur,
\new-line
is ignored,
and
\
must be used to quote the characters
\,
$,
`,
and the first character of
word.
If
-
is appended to
<<,
then all leading tabs are stripped from
word
and from the document.

<&digit

The standard input is duplicated from file descriptor
digit
(see
dup(2)).
Similarly for the standard output using
>& digit.

<&-

The standard input is closed.
Similarly for the standard output using
>&-.

<&p

The input from the co-process is moved to standard input.

>&p

The output to the co-process is moved to standard output.

If one of the above is preceded by a digit,
then the
file descriptor number referred to is that specified
by the digit
(instead of the default 0 or 1).
For example:

. . . 2>&1

means file descriptor 2 is to be opened
for writing as a duplicate
of file descriptor 1.

The order in which redirections are specified is significant.
The shell evaluates each redirection in terms of the
(file descriptor, file)
association at the time of evaluation.
For example:

. . . 1>fname 2>&1

first associates file descriptor 1 with file
fname .
It then associates file descriptor 2 with the file associated with file
descriptor 1 (i.e.
fname ).
If the order of redirections were reversed, file descriptor 2 would be associated
with the terminal (assuming file descriptor 1 had been) and then file descriptor
1 would be associated with file
fname .

If a command is followed by
&
and job control is not active,
then the default standard input
for the command
is the empty file
/dev/null.
Otherwise, the environment for the execution of a command contains the
file descriptors of the invoking shell as modified by
input/output specifications.

Environment.

The
environment
(see
environ(7))
is a list of name-value pairs that is passed to
an executed program in the same way as a normal argument list.
The names must be
identifiers
and the values are character strings.
The shell interacts with the environment in several ways.
On invocation, the shell scans the environment
and creates a
variable
for each name found,
giving it the corresponding value and marking it
export.
Executed commands inherit the environment.
If the user modifies the values of these
variables
or creates new ones,
using the
export
or
typeset-x
commands they become part of the
environment.
The environment seen by any executed command is thus composed
of any name-value pairs originally inherited by the shell,
whose values may be modified by the current shell,
plus any additions
which must be noted in
export
or
typeset-x
commands.

The environment for any
simple-command
or function
may be augmented by prefixing it with one or more variable assignments.
A variable assignment argument is a word of the form
identifier=value.
Thus:

TERM=450 cmd args and
(export TERM; TERM=450; cmd args)

are equivalent (as far as the above execution of
cmd
is concerned except for special commands listed below that are
preceded with a dagger).

If the
-k
flag is set,
all
variable assignment arguments are placed in the environment,
even if they occur after the command name.
The following
first prints
a=b c
and then
c:

echo a=b c
set -k
echo a=b c

This feature is intended for use with scripts written
for early versions of the shell and its use in new scripts
is strongly discouraged.
It is likely to disappear someday.

Functions.

The
function
reserved word, described in the
Commands
section above,
is used to define shell functions.
Shell functions are read in and stored internally.
Alias names are resolved when the function is read.
Functions are executed like commands with the arguments
passed as positional parameters.
(See
Execution
below.)

Functions execute in the same process as the caller and
share all files
and present working directory with the
caller.
Traps caught by the caller are reset to their default action
inside the function.
A trap condition that is not caught or ignored by the
function causes the function to terminate and the condition
to be passed on to the caller.
A trap on
EXIT
set inside a function
is executed after the function completes in the environment
of the caller.
Ordinarily,
variables are shared between the calling program
and the function.
However,
the
typeset
special command used within a function
defines local variables whose scope includes
the current function and
all functions it calls.

The special command
return
is used to return
from function calls.
Errors within functions return control to the caller.

Function identifiers
can be listed with the
-f
or
+f
option of the
typeset
special command.
The text of functions will also
be listed with
-f.
Functions can be undefined with the
-f
option of the
unset
special command.

Ordinarily,
functions are unset when the shell executes a shell script.
The
-xf
option of the
typeset
command allows a function to be exported
to scripts that are executed without a separate
invocation of the shell.
Functions that need to be defined across separate
invocations of the shell should be specified in the
ENV
file with the
-xf
option of
typeset.

Jobs.

If the
monitor
option of the
set
command is turned on,
an interactive shell associates a job with each pipeline.
It keeps
a table of current jobs, printed by the
jobs
command, and assigns them small integer numbers.
When a job is started asynchronously with
&,
the shell prints a line which looks
like:

[1] 1234

indicating that the job which was started asynchronously was job number
1 and had one (top-level) process, whose process id was 1234.

This paragraph and the next require features that are
not in all versions of UNIX and may not apply.
If you are running a job and wish to do something else you may hit the key
^Z (control-Z) which sends a STOP signal to the current job.
The shell will then normally indicate that the job has been `Stopped',
and print another prompt.
You can then manipulate the state of this job,
putting it in the background with the
bg
command, or run some other
commands and then eventually bring the job back into the foreground with
the foreground command
fg.
A ^Z takes effect immediately and
is like an interrupt in that pending output and unread input are discarded
when it is typed.

A job being run in the background will stop if it tries to read
from the terminal.
Background jobs are normally allowed to produce output,
but this can be disabled by giving the command ``stty tostop''.
If you set this
tty option, then background jobs will stop when they try to produce
output like they do when they try to read input.

There are several ways to refer to jobs in the shell.
A job can be referred to by the process id of any process of the job
or by one of the following:

%number

The job with the given number.

%string

Any job whose command line begins with
string.

%?string

Any job whose command line contains
string.

%%

Current job.

%+

Equivalent to
%%.

%-

Previous job.

The shell learns immediately whenever a process changes state.
It normally informs you whenever a job becomes blocked so that
no further progress is possible, but only just before it prints
a prompt.
This is done so that it does not otherwise disturb your work.

When the monitor mode is on, each background job that completes
triggers any trap set for
CHLD.

When you try to leave the shell while jobs are running or stopped, you will
be warned that `You have stopped(running) jobs.'
You may use the
jobs
command to see what they are.
If you do this or immediately try to
exit again, the shell will not warn you a second time, and the stopped
jobs will be terminated.

Signals.

The INT and QUIT signals for an invoked
command are ignored if the command is followed by
&
and the
monitor
option is not active.
Otherwise, signals have the values
inherited by the shell from its parent
(but see also
the
trap
special command below).

Execution.

Each time a command is executed, the above substitutions
are carried out.
If the command name matches one
of the
Special Commands
listed below,
it is executed within the
current shell process.
Next, the command name is checked to see if
it matches one of the user defined functions.
If it does,
the positional parameters are saved
and then reset to the arguments of the
function
call.
When the
function
completes or issues a
return,
the positional parameter list is restored
and any trap set on
EXIT
within the function is executed.
The value of a
function
is the value of the last command executed.
A function is also executed in the
current shell process.
If a command name is not a
special command
or a user defined
function,
a process is created and
an attempt is made to execute the command via
exec(2).

The shell variable
PATH
defines the search path for
the directory containing the command.
Alternative directory names are separated by
a colon
(:).
The default path is
/bin:/usr/bin:
(specifying
/bin,
/usr/bin,
and the current directory
in that order).
The current directory can be specified by
two or more adjacent colons, or by a colon
at the beginning or end of the path list.
If the command name contains a / then the search path
is not used.
Otherwise, each directory in the path is
searched for an executable file.
If the file has execute permission but is not a
directory or an
a.out
file,
it is assumed to be a file containing shell commands.
A sub-shell is spawned to read it.
All non-exported aliases,
functions,
and variables are removed in this case.
If the shell command
file doesn't have read permission,
or if the
setuid
and/or
setgid
bits are set on the file,
then the shell executes an agent whose job it is to
set up the permissions and execute the shell with the
shell command file passed down as an open file.
A parenthesized command is executed in
a sub-shell without removing non-exported quantities.

The text of the last
HISTSIZE
(default 128)
commands entered from a terminal device
is saved in a
history
file.
The file
$HOME/.sh_history
is used if the
HISTFILE
variable is not set
or if the file it names is not writable.
A shell can access the commands of
all
interactive
shells which use the same named
HISTFILE.
The special command
fc
is used to list or
edit a portion of this file.
The portion of the file to be edited or listed can be selected by
number or by giving the first character or
characters of the command.
A single command or range of commands can be specified.
If you do not specify an editor program as
an argument to
fc
then the value of the variable
FCEDIT
is used.
If
FCEDIT
is not defined then
/bin/ed
is used.
The edited command(s) is printed and re-executed upon
leaving the editor.
The editor name
-
is used to skip the editing phase and
to re-execute the command.
In this case a substitution parameter of the form
old=new
can be used to modify the command before execution.
For example, if
r
is aliased to
'fc-e-'
then typing
`r bad=good c'
will re-execute the most recent command which starts with the letter
c,
replacing the first occurrence of the string
bad
with the string
good.

In-line Editing Options

Normally, each command line entered from a terminal device is simply
typed followed by a new-line (`RETURN' or `LINE FEED').
If either the
emacs,
gmacs,
or
vi
option is active, the user can edit the command line.
To be in either of these edit modes
set
the corresponding
option.
An editing option is automatically selected each time the
VISUAL
or
EDITOR
variable is assigned a value ending in either of these
option names.

The editing features require that the user's terminal
accept `RETURN' as carriage return without line feed
and that a space (` ') must overwrite the current character on
the screen.
ADM terminal users should set the "space - advance"
switch to `space'.
Hewlett-Packard series 2621 terminal users should set the straps to
`bcGHxZ etX'.

The editing modes implement a concept where the user is looking through a
window at the current line.
The window width is the value of
COLUMNS
if it is defined, otherwise 80.
If the window width is too small to display the prompt and leave
at least 8 columns to enter input, the prompt is truncated from the
left.
If the line is longer than the window width minus two, a mark is
displayed at the end of the window to notify the user.
As the cursor moves and reaches the window boundaries the window will be
centered about the cursor.
The mark is a
> (<,*)
if the line extends on the
right (left, both) side(s) of the window.

The search commands in each edit mode provide access to the history file.
Only strings are matched, not patterns, although a leading
^
in the string restricts the match
to begin at the first character in the line.

This mode is entered by enabling either the
emacs
or
gmacs
option.
The only difference between these two modes is the way
they handle
^T.
To edit, the user
moves the cursor to the point needing correction and
then inserts or deletes characters or words as needed.
All the editing commands are control characters or escape
sequences.
The notation for control characters is caret (
^
) followed
by the character.
For example,
^F
is the notation for control
F.
This is entered by depressing `f' while holding down the
`CTRL' (control) key.
The `SHIFT' key is
not
depressed.
(The notation
^?
indicates the DEL (delete) key.)

The notation for escape sequences is
M-
followed by a
character.
For example,
M-f
(pronounced Meta f)
is entered by depressing ESC
(ascii
033)
followed by `f'.
(M-F
would be the notation for ESC followed by `SHIFT' (capital) `F'.)

All edit commands
operate from any place on the line
(not just at the beginning).
Neither the "RETURN" nor the "LINE FEED" key is
entered after edit commands except when noted.

^F

Move cursor forward (right) one character.

M-f

Move cursor forward one word.
(The
emacs
editor's idea of a word is a string of characters
consisting of only letters, digits and underscores.)

^B

Move cursor backward (left) one character.

M-b

Move cursor backward one word.

^A

Move cursor to start of line.

^E

Move cursor to end of line.

^]char

Move cursor forward to character
char
on current line.

M-^]char

Move cursor backward to character
char
on current line.

^X^X

Interchange the cursor and mark.

erase

(User defined erase character as defined
by the
stty(1)
command, usually
^H
or
#.)
Delete previous character.

^D

Delete current character.

M-d

Delete current word.

M-^H

(Meta-backspace) Delete previous word.

M-h

Delete previous word.

M-^?

(Meta-DEL) Delete previous word (if your interrupt character is
^?
(DEL, the default) then this command will not work).

^T

Transpose current character with next character in
emacs
mode.
Transpose two previous characters in
gmacs
mode.

^C

Capitalize current character.

M-c

Capitalize current word.

M-l

Change the current word to lower case.

^K

Delete from the cursor to the end of the line.
If preceded by a numerical parameter whose value is less than the
current cursor position, then delete from given position
up to the cursor.
If preceded by a numerical parameter whose value is greater than the
current cursor position, then delete from cursor up to
given cursor position.

^W

Kill from the cursor to the mark.

M-p

Push the region from the cursor to the mark on the stack.

kill

(User defined kill character as defined
by the stty command, usually
^G
or
@.)
Kill the entire current line.
If two
kill
characters are entered in succession, all
kill characters from then on cause a line feed
(useful when using paper terminals).

^Y

Restore last item removed from line. (Yank item back to the line.)

^L

Line feed and print current line.

^@

(Null character) Set mark.

M-space

(Meta space) Set mark.

^J

(New line) Execute the current line.

^M

(Return) Execute the current line.

eof

End-of-file character,
normally
^D,
is processed as an End-of-file only
if the current line is null.

^P

Fetch previous command.
Each time
^P
is entered
the previous command back in time is accessed.
Moves back one line when not on the first line of a multi-line command.

M-<

Fetch the least recent (oldest) history line.

M->

Fetch the most recent (youngest) history line.

^N

Fetch next command line.
Each time
^N
is entered
the next command line forward in time is accessed.

^Rstring

Reverse search history for a previous command line containing
string.
If a parameter of zero is given, the search is forward.
String
is terminated by a "RETURN" or "NEW LINE".
If string is preceded by a
^,
the matched line must begin with
string.
If
string
is omitted,
then the next command line containing the most recent
string
is accessed.
In this case a parameter of zero
reverses the direction of the search.

^O

Operate - Execute the current line and fetch
the next line relative to current line from the
history file.

M-digits

(Escape) Define numeric parameter, the digits
are taken as a parameter to the next command.
The commands that accept a parameter are
^F,
^B,
erase,
^C,
^D,
^K,
^R,
^P,
^N,
^],
M-.,
M-^],
M-_,
M-b,
M-c,
M-d,
M-f,
M-h,
M-l
and
M-^H.

M-letter

Soft-key - Your alias list is searched for an
alias by the name
_letter
and if an alias of this name is defined, its
value will be inserted on the input queue.
The
letter
must not be one of the above meta-functions.

M-[letter

Soft-key - Your alias list is searched for an
alias by the name
__letter
and if an alias of this name is defined, its
value will be inserted on the input queue.
The can be used to program functions keys on many terminals.

M-.

The last word of the previous command is inserted
on the line.
If preceded by a numeric parameter, the value
of this parameter determines which word to insert rather than
the last word.

M-_

Same as
M-..

M-*

Attempt file name generation on the current word.
An asterisk is appended if the word doesn't match any file
or contain any special
pattern characters.

M-ESC

File name completion.
Replaces the current word with the longest common prefix of all
filenames matching the current word with an asterisk appended.
If the match is unique, a
/
is appended if the file is a directory and a space is
appended if the file is not a directory.

M-=

List files matching current word pattern
if an asterisk were appended.

^U

Multiply parameter of next command by 4.

\

Escape next character.
Editing characters, the user's erase, kill and
interrupt (normally
^?)
characters
may be entered
in a command line or in a search string if preceded by a
\.
The
\
removes the next character's
editing features (if any).

^V

Display version of the shell.

M-\#

Insert a
\#
at the beginning of the line and execute it.
This causes a comment to be inserted in the history file.

There are two typing modes.
Initially, when you enter a command you are in the
input
mode.
To edit, the user enters
control
mode by typing ESC
(033)
and
moves the cursor to the point needing correction and
then inserts or deletes characters or words as needed.
Most control commands accept an optional repeat
count
prior to the command.

When in
vi
mode on most systems,
canonical processing is initially enabled and the
command will be echoed again if the speed is 1200 baud or greater and it
contains any control characters or less than one second has elapsed
since the prompt was printed.
The ESC character terminates canonical processing for the remainder of the command
and the user can then modify the command line.
This scheme has the advantages of canonical processing with the type-ahead
echoing of raw mode.

If the option
viraw
is also set, the terminal will always have canonical processing
disabled.
This mode is implicit for systems that do not support two
alternate end of line delimiters,
and may be helpful for certain terminals.

Input Edit Commands

By default the editor is in input mode.

erase

(User defined erase character as defined
by the stty command, usually
^H
or
#.)
Delete previous character.

^W

Delete the previous blank separated word.

^D

Terminate the shell.

^V

Escape next character.
Editing characters and the user's erase or kill
characters may be entered
in a command line or in a search string if preceded by a
^V.
The
^V
removes the next character's
editing features (if any).

\

Escape the next
erase
or
kill
character.

Motion Edit Commands

These commands will move the cursor.

[count]l

Cursor forward (right) one character.

[count]w

Cursor forward one alpha-numeric word.

[count]W

Cursor to the beginning of the next word that follows a blank.

[count]e

Cursor to end of word.

[count]E

Cursor to end of the current blank delimited word.

[count]h

Cursor backward (left) one character.

[count]b

Cursor backward one word.

[count]B

Cursor to preceding blank separated word.

[count]|

Cursor to column
count.

[count]fc

Find the next character c in the current line.

[count]Fc

Find the previous character c in the current line.

[count]tc

Equivalent to
f
followed by
h.

[count]Tc

Equivalent to
F
followed by
l.

[count];

Repeats
count
times,
the last single character find command,
f,
F,
t,
or
T.

[count],

Reverses the last single character find command
count
times.

0

Cursor to start of line.

^

Cursor to first non-blank character in line.

$

Cursor to end of line.

%

Moves to balancing
(,
),
{,
},
[,
or
].
If cursor is not on one of the above characters,
the remainder of the line is searched for the first
occurrence of one of the above characters first.

Search Edit Commands

These commands access your command history.

[count]k

Fetch previous command.
Each time
k
is entered
the previous command back in time is accessed.

[count]-

Equivalent to
k.

[count]j

Fetch next command.
Each time
j
is entered
the next command forward in time is accessed.

[count]+

Equivalent to
j.

[count]G

The command number
count
is fetched.
The default is the least recent history command.

/string

Search backward through history for a previous command containing
string.
String
is terminated by a "RETURN" or "NEW LINE".
If string is preceded by a
^,
the matched line must begin with
string.
If string is null the previous string will be used.

?string

Same as
/
except that search will be in the forward direction.

n

Search for next match of the last pattern to
/
or
?
commands.

N

Search for next match of the last pattern to
/
or
?,
but in reverse direction.
Search history for the string entered by the previous / command.

Text Modification Edit Commands

These commands will modify the line.

a

Enter input mode and enter text after the current character.

A

Append text to the end of the line.
Equivalent to
$a.

[count]cmotion

c[count]motion

Delete current character through the character that
motion
would move the cursor to and enter input mode.
If motion is
c,
the entire line will be deleted and
input mode entered.

C

Delete the current character through the end of line and enter input mode.
Equivalent to
c$.

[count]s

Delete
count
characters and enter input mode.

S

Equivalent to
cc.

D

Delete the current character through the end of line.
Equivalent to
d$.

[count]dmotion

d[count]motion

Delete current character through the character that
motion
would move to.
If motion is
d,
the entire line will be deleted.

i

Enter input mode and insert text before the current character.

I

Insert text before the beginning of the line.
Equivalent to
0i.

[count]P

Place the previous text modification before the cursor.

[count]p

Place the previous text modification after the cursor.

R

Enter input mode and
replace characters on the screen with characters you type overlay fashion.

[count]rc

Replace the
count
character(s) starting at the current cursor position with
c,
and advance the cursor.

[count]x

Delete current character.

[count]X

Delete preceding character.

[count].

Repeat the previous text modification command.

[count]~

Invert the case of the
count
character(s) starting at the current cursor position and advance the cursor.

[count]_

Causes the
count
word of the previous command to be appended and
input mode entered.
The last word is used
if
count
is omitted.

*

Causes an
*
to be appended to the current word and file name generation attempted.
If no match is found,
it rings the bell.
Otherwise, the word is replaced
by the matching pattern and input mode is entered.

\

Filename completion.
Replaces the current word with the longest common prefix of all
filenames matching the current word with an asterisk appended.
If the match is unique, a
/
is appended if the file is a directory and a space is
appended if the file is not a directory.

Other Edit Commands

Miscellaneous commands.

[count]ymotion

y[count]motion

Yank current character through character that
motion
would move the cursor to and puts them into the delete buffer.
The text and cursor are unchanged.

Y

Yanks from current position to end of line.
Equivalent to
y$.

u

Undo the last text modifying command.

U

Undo all the text modifying commands performed on the line.

[count]v

Returns the command
fc -e ${VISUAL:-${EDITOR:-vi}} count
in the input buffer.
If
count
is omitted, then the current line is used.

^L

Line feed and print current line.
Has effect only in control mode.

^J

(New line) Execute the current line, regardless of mode.

^M

(Return) Execute the current line, regardless of mode.

\#

If the first character of the command is a
\#,
then this command deletes this
\#
and each
\#
that follows a newline.
Otherwise,
sends the line after
inserting a
\#
in front of each line in the command.
Useful for causing the current line to be
inserted in the history as a comment and
removing comments from previous comment commands
in the history file.

=

List the file names that match the current word if an asterisk were
appended it.

@letter

Your alias list is searched for an
alias by the name
_letter
and if an alias of this name is defined, its
value will be inserted on the input queue for processing.

The following simple-commands are executed in the shell process.
Input/Output redirection is permitted.
Unless otherwise indicated, the output is written on file descriptor 1
and the exit status, when there is no syntax error, is zero.
Commands that are preceded by one or two §
are treated specially in the following ways:

1.

Variable assignment lists preceding the command
remain in effect when the command completes.

2.

I/O redirections are processed after variable assignments.

3.

Errors
cause a script
that contains them to abort.

4.

Words,
following a command preceded by §§
that are in the format of a variable assignment,
are expanded with the same rules as a variable assignment.
This means that
tilde substitution is performed after the
=
sign and word splitting and file name generation are not
performed.

§ : [ arg . . . ]

The command only expands parameters.

§ . file [ arg . . . ]

Read the complete
file
then execute the commands.
The commands are executed in the current Shell environment.
The search path
specified by
PATH
is used to find the directory containing
file.
If any arguments
arg
are given,
they become the positional parameters.
Otherwise the positional parameters are unchanged.
The exit status is the exit status of the last command executed.

§§ alias [ -tx ] [ name[ =value ] ] . . .

alias
with no arguments prints the list of aliases
in the form
name=value
on standard output.
An
alias
is defined
for each name whose
value
is given.
A trailing space in
value
causes the next word to be checked for
alias substitution.
The
-t
flag is used to set and list tracked aliases.
The value of a tracked alias is the full pathname
corresponding to the given
name.
The value becomes undefined when the value of
PATH
is reset but the aliases remained tracked.
Without the
-t
flag,
for each
name
in the argument list
for which no
value
is given, the name
and value of the alias is printed.
The
-x
flag is used to set or print exported aliases.
An exported alias is defined for scripts invoked by name.
The exit status is non-zero if a
name
is given, but no value, and no alias has been defined for the
name .

bg [ job . . . ]

This command is only on systems that support job control.
Puts each specified
job
into the background.
The current job is put in the background
if
job
is not specified.
See
Jobs
for a description of the format of
job.

§ break [ n ]

Exit from the enclosing
for ,
while ,
until ,
or
select
loop, if any.
If
n
is specified then break
n
levels.

§ continue [ n ]

Resume the next iteration of the enclosing
for ,
while ,
until ,
or
select
loop.
If
n
is specified then resume at the
n-th
enclosing loop.

cd [ arg ]

cdold new

This command can be in either of two forms.
In the first form it
changes the current directory to
arg.
If
arg
is
-
the directory is changed to the previous
directory.
The shell
variable
HOME
is the default
arg.
The variable
PWD
is set to the current directory.
The shell variable
CDPATH
defines the search path for
the directory containing
arg.
Alternative directory names are separated by
a colon
(:).
The default path is
<null>
(specifying the current directory).
Note that the current directory is specified by a null path name,
which can appear immediately after the equal sign
or between the colon delimiters anywhere else in the path list.
If
arg
begins with a / then the search path
is not used.
Otherwise, each directory in the path is
searched for
arg.

The second form of
cd
substitutes the string
new
for the string
old
in the current directory name,
PWD
and tries to change to this new directory.

The
cd
command may not be executed by
rsh .

echo [ arg . . . ]

See
echo(1)
for usage and description.

§ eval [ arg . . . ]

The arguments are read as input
to the shell
and the resulting command(s) executed.

§ exec [ arg . . . ]

If
arg
is given,
the command specified by
the arguments is executed in place of this shell
without creating a new process.
Input/output arguments may appear and
affect the current process.
If no
arguments are given
the effect of this command is to
modify file descriptors
as prescribed by the input/output redirection list.
In this case,
any file descriptor numbers greater than 2 that are
opened with this mechanism are closed when invoking
another program.

§ exit [ n ]

Causes the shell to exit
with the exit status specified by
n.
The value will be the least significant 8 bits of the specified status.
If
n
is omitted then the exit status is that of the last command executed.
When exit occurs when executing a trap, the last command refers
to the command that executed before the trap was invoked.
An end-of-file will also cause the shell to exit
except for a
shell which has the
ignoreeof
option (See
set
below) turned on.

§§ export [ name[ =value ] ] . . .

The given
names
are marked for automatic
export to the
environment
of subsequently-executed commands.

fc [ -eename ] [ -nlr ] [ first [ last ] ]

fc -e - [ old\=new ] [ command ]

In the first form,
a range of commands from
first
to
last
is selected from the last
HISTSIZE
commands that were typed at the terminal.
The arguments
first
and
last
may be specified as a number or as a string.
A string is used to locate the most recent command starting with
the given string.
A negative number is used as an offset to the current command number.
If the
-l
flag
is selected,
the commands are listed on standard output.
Otherwise, the editor program
ename
is invoked on a file containing these
keyboard commands.
If
ename
is not supplied, then the value of the variable
FCEDIT
(default
/bin/ed )
is used as the editor.
When editing is complete, the edited command(s)
is executed.
If
last
is not specified
then it will be set to
first.
If
first
is not specified
the default is the previous command
for editing and -16 for listing.
The flag
-r
reverses the order of the commands and
the flag
-n
suppresses command numbers when listing.
In the second form the
command
is re-executed after the substitution
old =new
is performed.

fg [ job . . . ]

This command is only on systems that support job control.
Each
job
specified is brought to the foreground.
Otherwise, the current job is
brought into the foreground.
See
Jobs
for a description of the format of
job.

getoptsoptstring name [ arg . . . ]

Checks
arg
for legal options.
If
arg
is omitted,
the positional parameters are used.
An option argument begins with a
+
or a
-.
An option not beginning with
+
or
-
or the argument
- -
ends the options.
optstring
contains the letters that
getopts
recognizes.
If a letter is followed by a
:,
that option is expected to have an argument.
The options can be separated from the argument by blanks.

getopts
places the next option letter it finds inside variable
name
each time it is invoked with a
+
prepended when
arg
begins with a
+.
The index of the next
arg
is stored in
OPTIND.
The option argument,
if any,
gets stored in
OPTARG.

A leading
:
in
optstring
causes
getopts
to store the letter of an invalid
option in
OPTARG,
and to set
name
to
?
for an unknown option and to
:
when a required option is missing.
Otherwise,
getopts
prints an error message.
The exit status is non-zero when there are no more options.

jobs [ -lnp ] [ job \. . . ]

Lists information about each given job; or all active jobs if
job
is omitted.
The
-l
flag lists process ids in addition to the normal information.
The
-n
flag only displays jobs that have stopped or exited since last
notified.
The
-p
flag causes only the process group to be listed.
See
Jobs
for a description of the format of
job.

kill [ -sig ] job . . .

kill-l

Sends either the TERM (terminate) signal or the
specified signal to the specified jobs or processes.
Signals are either given by number or by names (as given in
<signal.h>,
stripped of the prefix ``SIG'' with
the exception that SIGCHD is named CHLD).
If the signal being sent is TERM (terminate) or HUP (hangup),
then the job or process will be sent a CONT (continue) signal
if it is stopped.
The argument
job
can be the process id of a process that is not a member of one of the
active jobs.
See
Jobs
for a description of the format of
job.
In the second form,
kill -l,
the signal numbers and names are listed.

letarg . . .

Each
arg
is a separate
arithmetic expression
to be evaluated.
See
Arithmetic Evaluation
above, for a description of arithmetic expression evaluation.

The exit status is
0 if the value of the last expression
is non-zero, and 1 otherwise.

§ newgrp [ arg . . . ]

Equivalent to
exec /bin/newgrp arg . . . .

print [ -Rnprsu [ n ] ] [ arg . . . ]

The shell output mechanism.
With no flags or with flag
-
or
- -,
the arguments are printed
on standard output as described by
echo(1).
In raw mode,
-R
or
-r,
the escape conventions of
echo
are ignored.
The
-R
option will print all subsequent arguments and options
other than
-n.
The
-p
option causes the
arguments to be written onto the pipe
of the process spawned with
|&
instead of standard output.
The
-s
option causes the
arguments to be written onto the history file
instead of standard output.
The
-u
flag can be used to specify a one digit
file descriptor unit number
n
on which the
output will be placed.
The default is 1.
If the flag
-n
is used, no
new-line
is added to the output.
The exit status is 0 unless the output file is
not open for writing.

pwd

Equivalent to
print -r - $PWD

read [ -prsu [ n ] ] [ name?prompt ] [ name . . . ]

The shell input mechanism.
One line is read and
is broken up into fields using the characters in
IFS
as separators.
The escape character,
\,
is used to remove any special meaning for the next
character and for line continuation.
In raw mode,
-r,
the
\
character is not treated specially.
The first
field is assigned to the first
name,
the second field
to the second
name,
etc., with leftover fields assigned to the last
name.
The
-p
option causes the input line
to be taken from the input pipe
of a process spawned by the shell
using
|&.
If the
-s
flag is present,
the input will be saved as a command in the history file.
The flag
-u
can be used to specify a one digit file
descriptor unit
n
to read from.
The file descriptor can be opened with the
exec
special command.
The default value of
n
is 0.
If
name
is omitted then
REPLY
is used as the default
name.
The exit status is 0 unless the input file is
not open for reading or an end-of-file is encountered.
An end-of-file with the
-p
option causes cleanup for this process
so that another can be spawned.
If the first argument contains a
?,
the remainder of this word is used as a
prompt
on standard error
when the shell is interactive.
The exit status is 0 unless an end-of-file is encountered.

§§ readonly [ name[ =value ] ] . . .

The given
names
are marked
readonly and these
names cannot be changed
by subsequent assignment.

§ return [ n ]

Causes a shell
function
or
.
script to return
to the invoking script
with the return status specified by
n.
The value will be the least significant 8 bits of the specified status.
If
n
is omitted then the return status is that of the last command executed.
If
return
is invoked while not in a
function
or a
.
script,
then it is the same as an
exit.

set [ ±aefhkmnopstuvx ] [ ±ooption ]. . . [ ±Aname ] [ arg . . . ]

The flags for this command have meaning as follows:

-A

Array assignment.
Unset the variable
name
and assign values sequentially from the
list
arg.
If
+A
is used, the variable
name
is not unset first.

-a

All subsequent variables that are defined are automatically exported.

-e

If a command has a non-zero exit status,
execute the
ERR
trap, if set,
and exit.
This mode is disabled while reading profiles.

-f

Disables file name generation.

-h

Each command
becomes a tracked alias when first encountered.

-k

All variable assignment arguments are placed in the environment for a command,
not just those that precede the command name.

-m

Background jobs will run in a separate process group
and a line will print upon completion.
The exit status of background jobs is reported in a completion message.
On systems with job control,
this flag is turned on automatically for
interactive shells.

-n

Read commands and check them for syntax errors, but do not execute them.
Ignored for interactive shells.

-o

The following argument can be one of the following option names:

allexport

Same as
-a.

errexit

Same as
-e.

bgnice

All background jobs are run at a lower priority.
This is the default mode.

emacs

Puts you in an
emacs
style in-line editor for command entry.

gmacs

Puts you in a
gmacs
style in-line editor for command entry.

ignoreeof

The shell will not exit on end-of-file.
The command
exit
must be used.

keyword

Same as
-k.

markdirs

All directory names resulting from file name generation have a trailing
/
appended.

Puts you in insert mode of a
vi
style in-line editor
until you hit escape character
033.
This puts you in control mode.
A return sends the line.

viraw

Each character is processed as it is typed
in
vi
mode.

xtrace

Same as
-x.

If no option name is supplied then the current option settings are printed.

-p

Disables processing of the
$HOME/.profile
file and uses the file
/etc/suid_profile
instead of the
ENV
file.
This mode is on whenever the effective uid (gid)
is not equal to the real uid (gid).
Turning this off causes the effective uid and gid to be
set to the real uid and gid.

-s

Sort the positional parameters lexicographically.

-t

Exit after reading and executing one command.

-u

Treat unset parameters as an error when substituting.

-v

Print shell input lines as they are read.

-x

Print commands and their arguments as they are executed.

-

Turns off
-x
and
-v
flags and stops examining arguments for flags.

- -

Do not change any of the flags; useful in setting
$1
to a value beginning with
-.
If no arguments follow this flag then the positional parameters are unset.

Using
+
rather than
-
causes these flags to be turned off.
These flags can also be used upon invocation of the shell.
The current set of flags may be found in
$-.
Unless
-A
is specified,
the remaining arguments are positional
parameters and are assigned, in order, to
$1$2. . . .
If no arguments are given then the names and values
of all variables are printed on the standard output.

§ shift [ n ]

The positional parameters from
$n+1. . .
are renamed
$1. . .
, default
n
is 1.
The parameter
n
can be any arithmetic expression that evaluates to a non-negative
number less than or equal to
$#.

§ times

Print the accumulated user and system times for
the shell and for processes
run from the shell.

§ trap [ arg ] [ sig ] . . .

arg
is a command to be read and executed when the shell
receives signal(s)
sig.
(Note that
arg
is scanned once when
the trap is set and once when the trap
is taken.)
Each
sig
can be given as a number or as the name of the signal.
Trap commands are executed in order of signal number.
Any attempt to set a trap on a signal that
was ignored on entry to the current shell
is ineffective.
If
arg
is omitted or is
-,
then the trap(s) for each
sig
are reset
to their original values.
If
arg
is the null
string then this signal is ignored by the shell and by the commands
it invokes.
If
sig
is
ERR
then
arg
will be executed whenever a command has a non-zero exit status.
If
sig
is
DEBUG
then
arg
will be executed after each command.
If
sig
is
0
or
EXIT
and the
trap
statement is executed inside the body of a function,
then the command
arg
is executed
after the function completes.
If
sig
is
0
or
EXIT
for a
trap
set outside any function
then the command
arg
is executed
on exit from the shell.
The
trap
command
with no arguments prints a list
of commands associated with each signal number.

§§ typeset [ ±HLRZfilrtux [ n ] ] [ name[ =value ] ] . . .

Sets attributes and values for shell variables and functions.
When invoked inside a function,
a new instance of the variables
name
is created.
The variables value and type are restored
when the function completes.
The following list of attributes may be specified:

Left justify and remove leading blanks from
value.
If
n
is non-zero it defines the width
of the field,
otherwise it is determined by the width of the value of
first assignment.
When the variable is assigned to, it is
filled on the right with blanks or truncated, if necessary, to
fit into the field.
Leading zeros are removed if the
-Z
flag is also set.
The
-R
flag is turned off.

-R

Right justify and fill with leading blanks.
If
n
is non-zero it defines the width
of the field,
otherwise it is determined by the width of the value of
first assignment.
The field is left filled with blanks or
truncated from the end if the
variable is reassigned.
The
-L
flag is turned off.

-Z

Right justify and fill with leading zeros if
the first non-blank character is a digit and the
-L
flag has not been set.
If
n
is non-zero it defines the width
of the field,
otherwise it is determined by the width of the value of
first assignment.

-f

The names refer to function names rather than
variable names.
No assignments can be made and the only other
valid flags are
-t,
-u
and
-x.
The flag
-t
turns on execution tracing for this function.
The flag
-u
causes this function to be marked undefined.
The
FPATH
variable will be searched to find the function definition
when the function is referenced.
The flag
-x
allows the function definition to remain in effect across shell
procedures invoked by name.

-i

Parameter is an integer.
This makes arithmetic faster.
If
n
is non-zero it defines the output arithmetic base,
otherwise the first assignment determines the output base.

-l

All upper-case characters are
converted to lower-case.
The upper-case flag,
-u
is turned off.

-r

The given
names
are marked
readonly and these
names cannot be changed
by subsequent assignment.

-t

Tags the variables.
Tags are user definable and have no special
meaning to the shell.

-u

All lower-case characters are converted
to upper-case characters.
The lower-case flag,
-l
is turned off.

-x

The given
names
are marked for automatic
export to the
environment
of subsequently-executed commands.

The
-i
attribute can not be specified along with
-R,
-L,
-Z,
or
-f.

Using
+
rather than
-
causes these flags to be turned off.
If no
name
arguments are given but flags are specified,
a list of
names
(and optionally the
values )
of the
variables
which have these
flags set
is printed.
(Using
+
rather than
-
keeps the
values from being printed.)
If no
names
and flags
are given,
the
names
and
attributes
of all
variables
are printed.

ulimit [ -HSacdfmnpstv ] [ limit ]

Set or display a resource limit.
The available resources limits are listed below.
Many systems do not contain one or more of these limits.
The limit for a specified resource is set when
limit
is specified.
The value of
limit
can be a number in the unit specified below with each resource,
or the value
unlimited.
The
H
and
S
flags specify whether the hard limit or the
soft limit for the given resource is set.
A hard limit cannot be increased once it is set. A soft
limit can be increased up to the value of the hard limit.
If neither the
H
or
S
options is specified, the limit applies to both.
The current resource limit is printed when
limit
is omitted.
In this case the soft limit is printed unless
H
is specified.
When more that one resource is specified, then the limit
name and unit is printed before the value.

-a

Lists all of the current resource limits.

-c

The number of 512-byte blocks on the size of core dumps.

-d

The number of K-bytes on the size of the data area.

-f

The number of 512-byte blocks on files written by child processes (files of any size may be read).

-m

The number of K-bytes on the size of physical memory.

-n

The number of file descriptors plus 1.

-p

The number of 512-byte blocks for pipe buffering.

-s

The number of K-bytes on the size of the stack area.

-t

The number of seconds to be used by each process.

-v

The number of K-bytes for virtual memory.

If no option is given,
-f
is assumed.

umask [ mask ]

The user file-creation mask is set to
mask
(see
umask(2)).
mask
can either be an octal number or
a symbolic value as described in
chmod(1).
If a symbolic value is given,
the new
umask value is the complement of the result of
applying
mask
to the complement of the previous umask value.
If
mask
is omitted, the current value of the mask is printed.

unaliasname . . .

The
aliases
given by the list of
names
are removed from the
alias
list.

unset [ -f ] name . . .

The variables given by the list of
names
are unassigned,
i.e.,
their values and attributes are erased.
Readonly variables cannot be unset.
If the
-f,
flag
is set, then the names refer to
function
names.
Unsetting
ERRNO,LINENO,MAILCHECK,OPTARG,OPTIND,RANDOM,SECONDS,TMOUT,
and
_
removes their special meaning even if they are
subsequently assigned to.

§ wait [ job ]

Wait for the specified
job
and
report its termination status.
If
job
is not given then all currently active child processes are waited for.
The exit status from this command is that of
the process waited for.
See
Jobs
for a description of the format of
job.

whence [ -pv ] name . . .

For each
name,
indicate how it
would be interpreted if used as a command name.

The
-v
flag
produces a more verbose report.

The
-p
flag
does a path search for
name
even if name is an alias, a function, or a reserved word.

Invocation.

If the shell is invoked by
exec(2),
and the first character of argument zero
($0)
is
-,
then the shell is assumed to be a
login
shell and
commands are read from
/etc/profile
and then from either
.profile
in the current directory or
$HOME/.profile,
if either file exists.
Next, commands are read from
the file named by
performing parameter substitution on
the value of the environment variable
ENV
if the file exists.
If the
-s
flag is not present and
arg
is, then a path search is performed on the first
arg
to determine the name of the script to execute.
The script
arg
must have read permission and any
setuid
and
getgid
settings will be ignored.
If the script is not found on the path,
arg
is processed as if it named a builtin command or function.
Commands are then read as described below;
the following flags are interpreted by the shell
when it is invoked:

-c string

If the
-c
flag is present then
commands are read from
string.

-s

If the
-s
flag is present or if no
arguments remain
then commands are read from the standard input.
Shell output,
except for the output of the
SpecialCommands
listed above,
is written to
file descriptor 2.

-i

If the
-i
flag is present or
if the shell input and output are attached to a terminal (as told by
ioctl(2))
then this shell is
interactive.
In this case TERM is ignored (so that kill 0
does not kill an interactive shell) and INTR is caught and ignored
(so that
wait
is interruptible).
In all cases, QUIT is ignored by the shell.

-r

If the
-r
flag is present the shell is a restricted shell.

The remaining flags and arguments are described under the
set
command above.

Rsh
is used to set up login names and execution environments whose
capabilities are more controlled than those of the standard shell.
The actions of
rsh
are identical to those of
sh ,
except that the following are disallowed:

The restrictions above are enforced
after .profile and the
ENV
files are interpreted.

When a command to be executed is found to be a shell procedure,
rsh
invokes
sh
to execute it.
Thus, it is possible to provide to the end-user shell procedures
that have access to the full power of
the standard shell,
while imposing a limited menu of commands;
this scheme assumes that the end-user does not have write and
execute permissions in the same directory.

The net effect of these rules is that the writer of the
.profile
has complete control over user actions,
by performing guaranteed setup actions
and leaving the user in an appropriate directory
(probably
not
the login directory).

The system administrator often sets up a directory
of commands
(i.e.,
/usr/rbin)
that can be safely invoked by
rsh.

Errors detected by the shell, such as syntax errors,
cause the shell
to return a non-zero exit status.
Otherwise, the shell returns the exit status of
the last command executed (see also the
exit
command above).
If the shell is being used non-interactively
then execution of the shell file is abandoned.
Run time errors detected by the shell are reported by
printing the command or function name and the error condition.
If the line number that the error occurred on is greater than one,
then the line number is also printed in square brackets
([])
after the command or function name.

If a command which is a
tracked alias
is executed, and then a command with the same name is
installed in a directory in the search path before the directory where the
original command was found, the shell will continue to
exec
the original command.
Use the
-t
option of the
alias
command to correct this situation.

Some very old shell scripts contain a
^
as a synonym for the pipe character
|.

Using the
fc
built-in command within a compound command will cause the whole
command to disappear from the history file.

The built-in command .file
reads the whole file before any commands are executed.
Therefore,
alias
and
unalias
commands in the file
will not apply to any functions defined in the file.

Traps are not processed while a job is waiting for a foreground process.
Thus, a trap on
CHLD
won't be executed until the foreground job terminates.